People think of dinosaurs as huge animals that could peer over the tops of tall trees. But many dinosaurs were small. Some were about the size of young chickens, and some were not much bigger than the dinosaur tooth pictured at right. Obviously Noah wasn't going to stuff a pair of 30-meter high dinosaurs in the Ark. So what did he do?
Small dinosaurs would fit on the Ark easily. And remember that even the largest dinosaurs started their lives as younger and smaller babies. In the late 1970s, skeletons and eggs of some tiny juvenile Mussaurus dinosaurs were found in Patagonia in southern Argentina. Mussaurus means “mouse reptile”, and the name is apt because the best-preserved Mussaurus skeleton is so small it fits comfortably in a human hand.
New Scientist of 6 December, 2000 announced the discovery of fossils of the smallest known adult dinosaur. These “microraptors” were only 39 centimeters (15 inches) long — 24 centimeters (9½ inches) of which were its tail.
We don't know how many species of dinosaur that God sent to Noah to take on the Ark. If the largest types were included, it is possible they were taken when they were still youngish but able to mate. Many animals can mate long before they are fully grown. </sarcasm>
Genesis 6:19-20 "And of every living thing of all flesh you shall bring two of every sort into the ark, to keep them alive with you; they shall be male and female. Of the birds after their kind, of animals after their kind, and of every creeping thing of the earth after its kind, two of every kind will come to you to keep them alive."
Those were his instruction.